1. Field of the Invention
The field of this invention lies within the art of impact printing. Impact printing can take place by a hammer having a tip which impacts a ribbon to place a series of dots or a dot matrix format on an underlying media. The invention more specifically is directed toward hammerbanks of line printers having a series of hammers which are retained by a permanent magnet and are released for impact by an electrical coil which overcomes the permanent magnetism.
2. Background of the Invention and Prior Art
The prior art with respect to impact printers generally incorporates a number of impact printers of various designs and various configurations. One of the preferred types of impact printers are those impact printers referred to as line printers. The configuration of line printers is such where a hammerbank having a number of printing tips impacts a print ribbon overlying a media to be printed upon. The hammers are held and retained by a permanent magnet prior to being released for impact. The permanent magnet provides a certain amount of magnetic flux to the hammer in order to retain it. The flux required is dependent upon the size, form, configuration, and magnetic characteristics of the hammer.
In the design of hammerheads and the hammers in general, there are key elements with regard to maintaining sufficient flux to retain or pull down the hammers. At the same time consideration must be given in allowing the hammers to fire on a rapid and high impact basis.
The retention and return of the hammers is oftentimes referred to as the pull down force by the permanent magnets.
Other characteristics of the hammers must consider the natural frequency of the spring. This is a criteria as to the firing at a particular rate.
Another criteria is the pull down force required by the permanent magnets. Generally, as the mass of the hammerspring head increases, a greater stored energy can be maintained. However, as can be appreciated, this can be undesirable inasmuch as a greater mass of the head of the hammer can decrease the operational firing rate.
This invention is a significant improvement over the prior art by reason of the fact that it utilizes and replaces part of the hammerhead mass with shunt mass. This causes the hammerhead to be lighter and accelerate faster when released.
To the foregoing extent, the shunts or the fingers that are emplaced between the hammers allows the mass of the hammerhead to be reduced. At the same time the shunts help to maintain the pull down force or retention force by the permanent magnets. Therefore, the natural frequency of the spring can be increased allowing the spring to fire at an increased rate with the same impact energy.
Another improvement of this invention and an object thereof is to create a greater pull down force or retention force without an increase to the hammer mass. This allows the use of a stiffer spring thereby increasing stored energy in the spring. The net result is to increase the impact energy without a decrease in the firing rate.
Both of the foregoing aspects of the impact energy and the operational firing rate can be increased by a trade-off between the two. Thus, one skilled in the art can design the line printers of this invention in a manner to increase impact energy or firing rate. For instance, when multiple forms are being utilized, higher impact is required. On the other hand, when thinner forms are required and a greater speed or firing rate of the hammerbank is required, faster printing can take place.
Thus, with this invention, greater impact and faster firing rates can be accomplished as set forth hereinafter.
In summation, this invention comprises one or more hammerbank magnetic shunts emplaced between hammers in order to allow a larger magnetic flux to be applied to the bottom of the hammers of the hammerbank through the pole pieces than that flux required to saturate the hammerhead cross section.
More specifically, the invention incorporates the aspects of a hammer shunt plate made of a highly permeable magnetic material having fingers that are placed between the hammerheads. The flux leaving the bottom of the pole piece in a dual pole piece arrangement enters the bottom of the hammerhead. The quantity of flux entering the bottom of the hammerhead is beyond the saturation flux of the hammerhead cross section. This saturation causes an increase in the MMF drop along the hammerhead forcing the flux into the shunt fingers.
A key element is to cause the entire flux from the pole piece to enter the bottom of the hammerhead. It is this flux that creates a magnetic force pulling the hammer down. The use of the shunt fingers replaces part of the hammerhead mass with the shunt finger mass so that the hammerhead can be lighter and accelerate faster when released.
The invention can also allow a reduction of the mass of the hammerheads while maintaining pull down force. This increases the natural frequency of the spring force allowing the hammer to be fired at an increased rate.
On the other hand, a greater pull down force or retention can be achieved without an increase to the head mass providing for increased stored energy so that greater impact energy without a decrease in the operational firing rate can be accommodated.